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Published byLily Sheehan Modified over 3 years ago

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Kinetic Models Considered Jeremy Dyson Basel, Switzerland

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2 Introduction Selected core models for parent compounds & metabolites in soil and water-sediment studies Models can be applied to other studies, e.g. hydrolysis Models chosen as simple & sensible approaches to representing behaviour from pseudo-mechanistic to more pragmatic perspectives Models displayed in terms of: Integrated equations based on initial conditions Differential of above for solving new problems Differential equations without initial conditions Endpoint calculation (DT50/DT90) from parameters

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3 Outline The Core Models Single First Order Biphasic Models – Gustafson & Holden – Bi-Exponential – Hockey Stick Lag Phase Models – Modified Hockey Stick – Logistic Alternatives & Links to Leaching Models Conclusion

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4 Single First Order (SFO) Fixed Shape DT90 = 3.32 x DT50 Assumes microbes not limiting Degradation % Remaining

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5 Single First Order (SFO)

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6 Biphasic Models DT50 DT90 Generally: DT50s Shorter DT90s Longer

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7 Biphasic Models Some Causes of Biphasic Behaviour Aged sorption Non-linear sorption Declining microbial activity Spatial variations in field Seasonal changes in weather

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8 Gustafson & Holden (FOMC)

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9 Bi-Exponential (DFOP or FOTC)

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10 Hockey Stick (HS)

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11 Lag Phase Models Lag Phase

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12 Modified Hockey Stick

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13 Logistic

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14 Alternatives & Links to Leaching Models Alternatives models can be used, but: Needs to be justified, e.g. Michaelis-Menten kinetics Need to avoid, where possible: – Time-dependent endpoints – Concentration-dependent endpoints – Large number of parameters – Microbial population dynamics Avoid Timme et al. as already noted in Guideance Identify biphasic kinetics for use in leaching models Not possible, but can link to DFOP for estimation

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15 Alternatives & Links to Leaching Models

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16 Conclusion Core models able to handle most kinetics problems Hence focus on solving problems using these models

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